Paper PS-ThA8
Etching Mechanisms of Transparent Conducting Oxides by Hydrocarbon Plasmas

Thursday, November 10, 2016, 4:40 pm, Room 104B

Zinc oxide (ZnO) and tin-doped indium oxide (ITO) are some of the most promising transparent conducing oxides (TCOs) for optoelectronic devices such as solar panels and head-mounted liquid crystal displays. With the demand of high-resolution optoelectronic devices increasing in the market, more efficient fabrication technologies for sub-micron- or nano-scale patterning of TCOs are required. Reactive ion etching (RIE) is a key technology for such fine patterning of materials, which has been widely used in the fabrication of semiconductor devices. RIE processes for TCOs have been developed with non-corrosive gases such as CH_4. However, etching reactions and mechanisms of such processes are not fully understood yet. The goal of this study is therefore to clarify plasma-surface interactions of CH₄ based plasmas with TCOs.

It has been found in our earlier beam experiments that the etch rate of ZnO by energetic CH_x⁺ ions strongly depends on the amount of hydrogen (i.e., value of x) of each incident CH_x⁺ ion. The results have also shown that ZnO stores hydrogen after the surface was exposed to energetic hydrogen ions. The modified surface layer of ZnO, which we call a “hydrogen-embedded ZnO” layer, has a higher sputtering yield for incident (inert) ions. In this study, we have examined how hydrogen can be stored in a hydrogen-embedded ZnO layer, using ab initio calculations. It has been found that, when a hydrogen atom is introduced to the surface or bulk of ZnO, it forms a hydroxyl group and weakens the Zn-O bond, converting ZnO to ZnOH. The result indicates that, in terms of energy levels, ZnOH has a higher sputtering yield than ZnO. A similar discussion of hydrogen effects on ITO will be also given in this presentation.